Fiber optic cables have been widely employed to allow for the transmission of digital information over long distances and the need for such cables continues to grow both in the U.S. and internationally. The configuration and structure of these fiber optic cables provides better quality signal transmission than conventional cables as fiber optic cables are less likely to suffer degradation or signal loss during transmission over the cable length. However, the exponential growth of fiber optic cables has created challenges as to how to manage and install this new technology so that its capabilities can be easily provided to all areas. These cables are generally installed below ground and one solution that has emerged for their effective installation is a process called “micro-trenching.” Micro-trenching is a known process that allows fiber optic cables as well as other cables and pipes to be installed below ground at a significantly lower cost and with a relatively low-impact to the surrounding areas as compared to other installation processes.
In general, with micro-trenching, a small trench is cut in the ground, typically using a trenching machine that is capable of cutting through cement, asphalt, earth, etc. Once the micro-trench is created, a conduit such as a plastic sleeve can be inserted into the trench along its length. The conduit can be a continuous sleeve or can consist of multiple sections that are coupled together along the length of the trench. One or more fiber optic cables or pipes may then be housed in the conduit, which the conduit serves to provide protection therefore. Once the conduit and its contents are situated in the trench, a flowable composition or filler can be used to partially or completely fill the micro-trench and fix the conduit therein. Once the composition hardens and fills the trench, the conduit is securely fixed therein. Other micro-trenching processes involve laying the fiber optic cable in the trench without a conduit.
Micro-trenching may be formed in a subsurface or covering surface, such as a street, sidewalk or roadway, to form a trench. One or more conduits may then be disposed in the trench, which are configured to house items, such as fiber optic cables or the like which may be connected to different electronics in the area. Alternatively, pipes or other items can also or alternatively be placed in the trench. As mentioned above, the cables may be placed directly into the trench without any encapsulating conduit. The trench may then be filled with a flowable filler such as non-shrinking concrete, polymer resins or a grout. The flowable filler fills the trench and surrounds the conduit or cable. After the flowable filler has cured and hardened, a sealer can then be placed on top of the flowable filler to provide protection to the trench and also to minimize the visual impact of the micro-trenching process.
Current flowable fillers for micro-trenches generally consist of a cementitious grout material. An exemplary grout material known in the art is “Portland cement.” While Portland cement materials are most common, other materials such as a relatively high-alumina cement material, granulated blast furnace slag cement and slag/Portland cement blends are also well known for this type of application.
As is well known, fillers that utilize a cementitious grout have disadvantages. One disadvantage of current grout materials is that they can suffer shrinkage as they harden or over time, which can lead to relatively significant surface defects as well as to a relatively high amount of consolidation both of which are too significant for success as a micro-trench grout application. This can also leave the conduit and the fiber optic cables housed therein unprotected and susceptible to damage. The same applies to fiber optic cables disposed directly into the trench.
Due to the issues associated with cementitious grout materials, other fillers for micro-trenching have been explored, but they also suffer from some limitations. For example, a recent proposal for a new micro-trenching method involves forming a trench in the pavement alone. In other words, the trench would be cut into the pavement and not the underlying substrate. The resulting trench would thus be very shallow, such as on the order of three (3) inches. After the trench is cut, one or more fiber optic cables would be laid into the trench. Thereafter, polyurea filler would be inserted into to the trench to fill it up to a level below the road surface. The filler would serve to hold the fiber optic cables in place and fill in the trench. An asphalt sealer could then be utilized to fill in the remainder of the trench and then match the trench surface with the surrounding roadway.
A couple of significant disadvantages have arisen with regard to this proposed technique. The resulting trench is unsuitable for the fiber optic cables because forming the trench and/or the polyurea filler can create issues with the foundation of the road. Specifically, the polyurea filler is substantially stronger than prior grout fillers and is actually stronger than the surrounding road which can affect the foundation of the surrounding road. Additionally, as many micro-trenching operations create part of the trench in the underlying substrate, this can create some problems as polyurea does not form a bond with the underlying substrate. Moreover, the cost of the polyurea material is very high. Further, polyurea material has a much shorter cure time than a cementitious grout material, which can be problematic in keeping the conduit for the fiber optic cables in place as it can expand due to heat before the polyurea filler has cured completely. For example, a polyurea can begin to harden within three minutes of placement and may be fully cure within 20 minutes. As is also known, conduits can expand up to 20-30% in length after curing which may cause the conduit to be pushed up to above the surface thereby exposing the fiber optic cables and conduit to damage. To overcome this issue, an additional clipping step must be performed to anchor the conduit within the trench. Moreover, as polyurea has a very low viscosity, using it to fill trenches formed in a non-planar surface, such as a hill or the like, can create filling issues. In other words, the polyurea filler may flow out of the trench. Lastly, existing sealers can be difficult to bond to a polyurea filler.
Thus, there is a need and desire for a filler system for use with micro-trench applications that overcomes the disadvantages with existing systems.